Looks like a job for the quadratic formula. ( discriminant says two real roots )

X = - b (+/-) sqrt(b^2-4ac)/2a

a = 1

b= - 3

c = - 13

X = - (- 3) (+/-) sqrt[(-3)^2 - 4(1)(- 13)]/2(1)

X = 3 (+/-) sqrt(9 + 52)/2

X = 3 (+/-) sqrt(61)/2

------exact

X = ~ 5.41

X = ~ - 2.41

X = - b (+/-) sqrt(b^2-4ac)/2a

a = 1

b= - 3

c = - 13

X = - (- 3) (+/-) sqrt[(-3)^2 - 4(1)(- 13)]/2(1)

X = 3 (+/-) sqrt(9 + 52)/2

X = 3 (+/-) sqrt(61)/2

------exact

X = ~ 5.41

X = ~ - 2.41